Video content may be encoded using various encoding techniques. Today there are many different types of display devices that may eventually display encoded video content. These different display devices include televisions having different aspect ratios (e.g., a 16:9 aspect ratio or a 4:3 aspect ratio) or different screen resolutions (e.g. 480 vertical lines of resolution or 1080 vertical lines of resolution), computer monitors having different aspect ratios and/or picture resolutions, and portable video players with various aspect ratios and different screen resolutions. The use of the display may also include using only a sub-regions of such display devices rather than filling the entire display with a single video content stream (e.g., “picture-in-picture” or display in a “window” on a computer screen). At the time the video content is encoded, it may not be known which display types may eventually display the video content, and the same encoded content may be used in a wide variety of display environments.
FIG. 1 illustrates a conventional system 100 for processing and distributing video content. The video content is captured using a video camera 102 (or any other video capture device) that transfers the captured video content onto video tape or another storage medium. Later, the captured video content may be edited using a video editor 104. A video encoder 106 encodes the video content to reduce the storage space required for the video content and/or to reduce the transmission bit rate required to transmit the video content. Various encoding techniques may be used to compress the video content, such as the MPEG-2 (Moving Picture Experts Group 2nd generation) compression format.
The encoded video content is provided to a transmitter 108, which transmits the encoded video content to one or more receivers 110 across a communication link 112. Communication link 112 may be, for example, a physical cable, a satellite link, a terrestrial broadcast, an Internet connection, a physical medium (such as a digital versatile disc (DVD)) or a combination thereof. A video decoder 114 decodes the signal received by receiver 110 using the appropriate decoding technique. The decoded video content is then displayed on a video display 116, such as a television or a computer monitor. Receiver 110 may be a separate component (such as a set top box) or may be integrated into video display 116. Similarly, video decoder 114 may be a separate component or may be integrated into the receiver 110 or the video display 116.
Video content may be captured and encoded into a format having a particular aspect ratio (such as 16:9) and later displayed on a video display having a different aspect ratio (such as 4:3). Various methods are available for displaying an image on a video display having a different aspect ratio. FIGS. 2A and 2B illustrate two possible methods for displaying an image having a 4:3 aspect ratio on a video display having a 16:9 aspect ratio. In FIG. 2A, a 16:9 video display 200 is not completely filled by the 4:3 image (located between the broken lines). Thus, blank side bars 202 are located on opposite sides of video display 200.
Another alternative for displaying a 4:3 image on a 16:9 video display is shown in FIG. 2B. In this situation, the width of the 4:3 image is expanded horizontally to align with the sides of the 16:9 video display 200. However, this expansion causes the top and bottom portions of the image to extend past the physical limits of video display 200. Thus, top and bottom portions 210 of the image are not displayed on video display 200.
FIGS. 2C and 2D illustrate methods for displaying an image having a 16:9 aspect ratio on a video display having a 4:3 aspect ratio. In FIG. 2C, a video display 250 has a 4:3 aspect ratio. The 16:9 image 252 is positioned between the two broken lines. Since the aspect ratio of the image is different from the aspect ratio of video display 250, two blank bars 254 are created across the top and bottom of the video display. The display format shown in FIG. 2C is commonly referred to as “letterboxing.”
In FIG. 2D, the height of the 16:9 image is expanded vertically to align with the top and bottom edges of the 4:3 video display 250. However, this expansion causes the sides of the image to extend past the physical limits of video display 250. Thus, side portions 260 of the image are not displayed on video display 250. The display format shown in FIG. 2D is commonly referred to as “overscanning” or “pan and scan.”
In existing video encoding systems, the encoded video content includes an indication of how to display the encoded video image on different types of displays. For example, if a video image has a 16:9 aspect ratio, the encoded video image includes information regarding how to display the video image on a video display having a 4:3 aspect ratio or a 2.3:1 aspect ratio. However, the information for each different type of video display (e.g., different aspect ratios) has a single option for displaying the image on that type of video display. Existing systems do not support multiple different image display regions that are specified in the video content stream and associated with a particular type of video display. For example, these different image display regions may focus on different characters appearing in the video content. Although existing systems allow a user to select among different pre-defined display formats (such as letterboxing or overscanning), these systems do not support multiple different encoder-specified image display regions, as described herein. Typically, if multiple display regions are specified, they are pre-defined display formats that are defined in the decoder rather than being transmitted with the video content stream.
Additionally, if a portion of an image is to be deleted after decoding (for example, because the output of the decoder is not a multiple of the fundamental “macroblock” dimensions used to represent the video in a compressed domain), existing video encoding systems typically delete content along the right edge of the image and/or along the bottom edge of the image. These systems may not provide the ability to specify which portion of the image to discard if a portion of the image needs to be deleted. Instead, these systems can only delete the portion of the image along the right edge or the bottom edge. Existing systems do not provide support for multiple different image framings for a given display type combined with the ability to delete specific portions of the image.
The systems and methods described herein address the above limitations by providing a system that encodes video content such that a user of a video display can select among multiple image framings for displaying the encoded image on the video display. Moreover, the video encoding systems and methods described herein are capable of specifying the particular portion of an image to be deleted if a portion of the image needs to be discarded.